The invention relates to admixtures of thermoplastic polyurethane base polymers and fluorinated additives that resist surface dulling and their use in the manufacture of articles, such as implantable medical devices.
Various fluorochemicals have been used to impart water and oil repellency, as well as soil resistance, to a variety of substrates. These fluorochemicals have most often been applied topically (for example, by spraying, padding, or finish bath immersion). The resulting repellent substrates have found use in numerous applications where water and/or oil repellency (as well as soil resistance) characteristics are valued, such as in protective garments for medical technicians and laboratory workers.
Certain low molecular weight fluorinated additives have been used in admixture with base polymers to impart water and oil repellency and/or hemocompatibility. When admixed with a base polymer, the fluorinated additives are sized accordingly to permit migration within, and blooming to the surface of, the base polymer. The advantage of this technical approach is that the surface properties of a polymer can be modified without significantly compromising the properties (e.g., elasticity or tensile strength) of the underlying base polymer. For the fluorinated additives to bloom to the surface of a base polymer, they are manufactured to be relatively small (e.g., typically less than 10,000 Daltons, depending upon the composition of the fluorinated additive and composition of the base polymer).
For particular applications, such as blood dwelling medical devices, it is desirable that the fluorinated additive be modified to avoid compromising the esthetically unpleasing appearance and dulling appearance of the product. We have discovered that this dulling can be controlled by reducing the amount of a specific species called trimer.